SPF Before answering this, we should first tell you what the SPF number means. SPF stands for sun protection factor and it essentially is a rating of how much UV light will be blocked. In general, a higher SPF number offers more protection from UV exposure than a lower number. How effective it is depends on many factors but the number one factor is your skin type. SPF 15 means that if you would normally burn after being in the sun for 20 minutes, you will be able to stay in the sun for 15 times as long or 5 hours. But it is important to note that the SPF scale is not a linear one. An SPF 2 will block 50% of the UV light while an SPF 15 will block 92% of all the UV light that reaches your skin and an SPF 34 blocks 97% of the UV light.
Although skin type is the number one factor is determining the effectiveness of a sunscreen, it is not the only factor. The intensity of the sun and the amount that you apply is also important. It’s this second factor that is most relevant to your question.
SPF 15, 30 or more
For cosmetic chemists, creating a great sunscreen is a balance between making a product that is effective and making one that feels good on the skin. If it were just a matter of effectiveness, everyone would create SPF 50 products or higher. But the problem with creating a higher SPF product is that for each number you go up, you increase the greasy, nasty feel on your skin. An SPF 15 feels much better than an SPF 30. And an SPF 100 is, well, gross.
Of course, the point of a sunscreen is to protect you from UV damage so you need to use an SPF sunblock with a high enough number to give you good protection.
Experts at the FDA have suggested that an sPF 15 is the minium that you should be using to protect your skin from UV damage. In testing these sunscreens have been shown to provide adequate protection when combined with limiting your time in the sun, wearing sun protective clothes. And an SPF 15 also can be made so it doesn’t feel excessively greasy.
SPF 15 is not enough
While the experts say SPF 15 scores high enough in testing to give protection, that is only true if you are applying the right amount. In testing, scientists use 2 mg/cm2 of skin. So, do people apply this much?
In a word…no. It is well known that people typically apply much less than the amount tested by sunscreen manufacturers.
Think about how much you use. If you were applying 2 mg/cm2 of sunscreen, your skin should feel greasy, slippery, and some of the sunscreen will be running off your skin. For an average sized person, you would need to apply about 30 mL of sunscreen per application. One bottle wouldn’t even be enough for a week at the beach.
So, while technically an SPF 15 will work (and it’s certainly better than nothing), it requires much more than you apply now. A good rule of thumb is that your sunscreen will be 1/3 as effective as the number based on the way people typically apply the product. That means an SPF 15 will protect you like a lab tested SPF 5. An SPF 30 will give SPF 10 protection in real life application.
Therefore, unless you going to glop on a lot more SPF sunblock than you are using now, you should stick with an SPF 30 or higher. This will give you the best chance at preventing sunburns and UV induced rosacea flare ups.
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